Organophosphorus and carbamate resistance in the predacious miteTyphlodromus pyri due to insensitive acetylcholinesterase

Abstract

The cause of parathion and propoxur resistance inTyphlodromus pyri was studied in a Dutch strain in which resistance was dependent on a semi-dominant gene. Activity of glutathione S-transferase and acetylcholinesterase and reaction rate of acetylcholinesterase with paraoxon and propoxur were measured in this resistant (R) and in a susceptible (S) strain. The R strain was 100-fold resistant to parathion and 2300-fold resistant to propoxur. A 36-fold reduction was found in rate of inhibition of acetylcholinesterase in the R strain for paraoxon, and a 14-fold reduction for propoxur. In combination with the monogenic nature of the resistance, this proves that the insensitivity of acetylcholinesterase is the cause of resistance. The rate constant of acetylcholinesterase inhibition at 25°C in the S and R strains was 1.5×105 and 4.2×103 M −1 min−1 respectively for paraoxon, and 5.1×104 and 3.6×103 M −1 min−1 for propoxur. There was no significant difference between the R and S strains in glutathione S-transferase activity. The R strain had a somewhat lower acetylcholinesterase activity than the S strain.